Write/read device for communication with transponders, having first coding means and second coding means

ABSTRACT

A write/read device ( 1 ) for the contactless communication with at least one transponder has first coding means ( 4 ) for coding a data block (DB) in accordance with a first coding method, which first coding means ( 4 ) can generate at the most a given number of N coding signals (KI) per data block (DB) in accordance with this first coding method, and has second coding means ( 9 ) for coding a data block (DB) in accordance with a second coding method, which second coding means ( 9 ) can generate at the most a given number of M coding signals (KI) per data block (DB) in accordance with this second coding method, and has selection means ( 10 ) for the selection between the coding signals (KI) supplied by the first coding means ( 4 ) and the coding signals (KI) supplied by the second coding means ( 9 ).

[0001] The invention relates to a write/read device designed for thecontactless communication with at least one transponder and comprisingdata supply means for supplying at least one data block and includingfirst coding means, by which first coding means a data block supplied bythe data supply means and applied to said first coding means can becoded in accordance with a first coding method and by which, as a resultof the coding in accordance with this first coding-method, at the most agiven number N of coding signals representing a data block can begenerated and supplied, and including carrier signal generating meansfor generating a carrier signal and including modulation means, to whichmodulation means the carrier signal and the coding signals can beapplied and by which modulation means the carrier signal can bemodulated in accordance with the coding signals so as to generate andsupply a modulated carrier signal corresponding to the number of codingsignals and having the same number of modulation steps, and includingtransmission means, to which transmission means the modulated carriersignal can be applied in order to be transmitted to at least onetransponder.

[0002] Such write/read device is commercially available in a variety ofversions and is consequently known. The known write/read device includescoding means adapted to perform a bit-oriented coding method, whereinfor coding a data block a given number N of bits can be coded, i.e. eachbit can exhibit either the logic zero state or the logic one state, sothat as a result of coding in accordance with this bit-oriented codingmethod at the most a given number N of coding signals, i.e. codingpulses, which represent a data block can be generated. Such abit-oriented coding method has the advantage that a component hightransmission rate is attainable. However, such a coding method entailsthe problem that corresponding to each coding signal a modulation stepoccurs in the carrier signal, which is amplitude-modulated in the knownwrite/read device, as a result of which during the transmission from thewrite/read device to a transponder not only the amplitude-modulatedcarrier signal has a comparatively high amplitude but that, in addition,the amplitudes in the so-called sidebands may exhibit comparativelylarge values if many modulation steps occur, which in many countriesgives rise to problems as regards statutory regulations relating tospurious emission and the limitation of spurious emission.

[0003] It is an object of the invention to preclude the afore-mentionedproblems in a write/read device and to provide an improved write/readdevice during whose use no problems arise as regards statutoryregulations relating to spurious emission and the limitation of spuriousemission. According to the invention this object is achieved in awrite/read device of the type defined in the opening paragraph in thatthere have been provided second coding means, by which second codingmeans a data block supplied by the data supply means and applied to saidsecond coding means can be coded in accordance with a second codingmethod and by which second coding means, as a result of coding inaccordance with said second coding method, at the most a given number Mof coding signals representing a data block can be generated andsupplied, the number M being smaller than the number N, and there havebeen provided selection means with the aid of which it is possible toselect that the coding signals representing a data block and supplied bythe first coding means or that the coding signals representing a datablock and supplied by the second coding means can be applied to theamplitude modulation means. By means of the measures in accordance withthe invention it is achieved in a very simple manner and with onlyminimal additional cost that in a write/read device in accordance withthe invention it is possible to choose from two coding possibilities orcoding methods, so that it is possible either to select a coding methodin which high amplitudes can occur in the range of the sidebands butwhich has the advantage that it guarantees high transmission rates, i.e.a transmission which is as rapid as possible, or to select anothercoding method which only allows a lower transmission rate, i.e. a slowertransmission, but which has the advantage that it guaranteesparticularly small amplitude values in the range of the sidebands,thereby ensuring that problems as regards statutory regulations relatingto maximum permissible spurious emissions and the limitation of spuriousemission are avoided.

[0004] In a write/read device in accordance with the invention themeasures defined in claim 3 have proved to be advantageous because it isthus the desired result is obtained with a minimal number of modulationsteps in the modulated carrier signal per coded data block, whichguarantees particularly small amplitude values in the range of thesidebands.

[0005] Various possibilities are available for the implementation of theselection means in a write/read device in accordance with the invention.However, it has proved to be particularly advantageous if the measuresdefined in claim 4 are taken because this has appeared to beparticularly favorable for implementation by means of a microcomputer.

[0006] The measures defined in claims 5 and 6 have proved to be veryadvantageous because they guarantee that in a transponder whichcommunicates with a write/read device in accordance with the inventionthe coding method selected for the data transmission in the write/readdevice can be detected very simply and thus a correct decoding isguaranteed in the transponder.

[0007] The afore-mentioned as well as further aspects of the inventionwill become apparent from the example of an embodiment describedhereinafter and will be elucidated with reference to this example.

[0008] The invention will be described in more detail with reference tothe drawings, which show two embodiments given by way of example, towhich the invention is not limited.

[0009]FIG. 1 is a block diagram of a relevant part of a write/readdevice in accordance with a first embodiment of the invention.

[0010]FIG. 2A shows an example of a data block which occurs in thedevice of FIG. 1.

[0011]FIGS. 2B to 2E show signals and signal waveforms which occur inthe device of FIG. 1 as a result of the data block shown in FIG. 2A.

[0012]FIG. 3 shows a write/read device in accordance with a secondembodiment of the invention.

[0013]FIG. 1 shows a write/read device 1, hereinafter briefly referredto as the device 1. The device 1 is designed for the contactlesscommunication with a plurality of transponders, as is known since long.

[0014] The device 1 includes data supply means 2, which in the presentcase are formed by a memory. However, the data supply means 2 mayalternatively be formed by other means, for example by data generationmeans which generate and supply data in response to information appliedto these means. The data supply means 2 are adapted to supply at leastone data block DB. Such a data block DB can be formed by, for example,the data block E1 hex=225 dec, as shown in FIG. 2A. This data block canbe represented in a binary manner by means of one byte if eight bits intotal. The following description is based on this example. However, itis to be noted that in the case that a data block corresponding to adecimal number having far more digits, this has the consequence that abinary representation of this block is possible only by means of aplurality of bytes having eight bits.

[0015] The device 1 includes a microcomputer 3 by means of which amultitude of means and functions are realized but in the present caseonly the relevant means will be described in more detail.

[0016] The first coding means 4 are implemented by means of themicrocomputer 3. The first coding means 4 make it possible to code adata block DB, which is supplied by the data supply means 2 and isapplied to the first coding means 4 via a data input DI of themicrocomputer 3, in accordance with a first coding method. The datainput DI is shown as a serial input but it can also take the form of aparallel input. The first coding means 4 are adapted to carry out abit-oriented coding method. In the present case the first coding means 4are adapted to perform a coding method in accordance with aReturn-To-Zero code. As a result of the coding in accordance with thisfirst coding method the first coding means 4 can generate and supply atthe most a number N of coding signals representing a data block DB. Inthe present case the number N has the value N=8 and the coding signalsare formed by coding pulses KI, as can be seen in FIG. 2B.

[0017] In the case that the first coding means 4 receive a data block DBcorresponding to the decimal number “225” (225 dec) from the data supplymeans 2, the first coding means 4 supply a total of coding pulses KI, asis shown in FIG. 2B, namely the coding pulses KI1, KI6, KI7 and KI8. Inthis respect it is to be noted that the coding pulse KI1 corresponds tothe value 2⁰, a coding pulse KI2 to the value 2¹, a coding pulse KI3 tothe value 2², a coding pulse KI4 to the value 2³, a coding pulse KI5 tothe value 2⁴, the coding pulse KI6 to the value 2⁵, the coding pulse KI7to the value 2⁶, and the coding pulse KI8 to the value 2⁷. Each of thesecoding pulses KI has a duration of 9.44 μs. The coding pulses KI aresituated in a time frame comprising eight time frame portions, whicheach have a frame portion time T1 of 37.76 μs. The coding pulses KI eachtime appear at the end of a frame time portion.

[0018] As regards the first coding means 4 it is to be noted that thesemeans 4 are adapted to generate a first start signal SP1 whichidentifies the first coding method and which is supplied by the firstcoding means 4 before the coding signals KI which represent a datablock, the number of coding signals being at the most equal to the givennumber N=8. The first start signal SP1 has a duration of 10.88 μs. Thisduration of 18.88 μs of the first start signal SP1 is characteristic ofthe first coding method that can be carried out by the first codingmeans 4. Similarly to the coding pulses KI, the first start signal SP1appears at the end of a time frame portion.

[0019] The device 1 further includes carrier signal generating means 5for generating a carrier signal TS, which in the present case is acarrier signal having a frequency of 13.56 MHz.

[0020] The device 1 further includes modulation means, which in thepresent case are formed by amplitude modulation means 6. The amplitudemodulation means 6 are arranged to receive the carrier signal TS and thecoding signals, i.e. the coding pulses KI. With the aid of the amplitudemodulation means 6 the carrier signal TS can be modulated in accordancewith the coding pulses KI, so as to generate and supply anamplitude-modulated carrier signal TSM having a number of modulationsteps MS equal to the number of coding pulses KI.

[0021] In the present case in accordance with FIGS. 2A and 2B a total offour modulation steps occur in the amplitude-modulated carrier signalTSM, which are referenced MS1, MS6, MS7 and MS8 in FIG. 2C. Similarly tothe coding pulses KI, the modulation steps MS are each time situated atthe end of a frame time portion and advantageously occupy only half theduration of a frame time portion, which is favorable in view of minimalamplitude values in the range of the sidebands of theamplitude-modulated carrier signal TSM. The modulation step in theamplitude-modulated carrier signal TSM which corresponds to the firststart signal SP1 bears the reference MS0. The modulation depth isrepresented only diagrammatically in FIG. 2C. In practice, it isadvantageous to use a 10% amplitude modulation (ASK 10%). However, it isalternatively possible to use an ASK of 20%, an ASK of 30% or an ASK of50%.

[0022] As is further apparent from fog 2C, the amplitude-modulatedcarrier signal TSM corresponding to the data block DB=225 dec requires atransmission time of 302.08 μs. This means that the transmission of thisamplitude-modulated carrier signal TSM and thus the transmission of thedata word DW=225 dec from the device 1 to a transponder whichcommunicates with the device 1 requires only a comparatively shortlength of time. However, owing to the occurrence of, in the presentcase, four modulation steps MS 1, MS6, MS7 and MS8 within thetransmission time interval of 302.08 μs comparatively high amplitudevalues will occur in the range of the sidebands of the carrier signalTS. If all the eight modulation steps MS1 to MS8 occur the maximumamplitude values are reached in the range of the sidebands of thecarrier signal TS.

[0023] The device 1 finally comprises transmission means 7, whichinclude a transmission coil 8. The transmission means 7 are arranged toreceive the amplitude-modulated carrier signal TSM. The transmissionmeans 7 transmit the amplitude-modulated carrier signal TSM inductivelyto receiving means of a transponder which is in communication with thedevice 1.

[0024] The device 1 advantageously includes second coding means 9 withthe aid of which a data block DB supplied by the data supply means 2 andapplied to the second coding means 9 can be coded in accordance with asecond coding method. The second coding means 9 are adapted to carry outa byte-oriented coding method. In the present case the second codingmeans 9 are adapted to carry out a coding method in accordance with a“1-out-of-K” code. Owing to the coding in accordance with this secondcoding method the second coding means 9 can generate and supply at themost a given number M of coding signals which represent a data block DB,the number M being smaller than the number N. In the present case thissecond coding method enables at the most the given number M=1 of codingsignals which represent a data block DB to be generated and supplied andthe second coding means 9 supply coding signals in the form of codingpulses KI, as is apparent from FIG. 2D.

[0025] As is further apparent from FIG. 2D, the second coding means 9 inthe present example, in which the data block DB=225 dec shown in FIG.2A, supply a single coding pulse KI225. The coding pulse KI225 issituated in a time frame comprising 256 time frame portions, which eachhave a frame portion time T2 of 18.88 μs. The coding pulse KI225 issituated in the 225th time frame portion, namely in such a way that itlies at the end of this time frame portion and continues till the end ofthis time frame portion. The coding pulse KI225 has a duration of 9.44μs, which corresponds to half the frame portion time T2 and which alsoapplies to all the other possible coding pulses KI1 to KI256. The codingpulse KI225 which can be supplied by the second coding means 9corresponds to one byte comprising eight (8) bits, namely the byte“10000111”, corresponding to the coding pulses KI1, KI6, KI7 and KI8which can be supplied by the first coding means 4.

[0026] As regards the second coding means 9 it is to be noted that thesecond coding means 9 are adapted to generate a second start signal SP2which is characteristic of the second coding method, which startsignal—as can be seen in FIG. 2D—is supplied by the second coding means9 before the coding signals which represent a data block, i.e. thecoding pulse KI225, the number of coding signals being at the most equalto the given number M=1.

[0027] With respect to the coding means 9 it is to be noted further thatthe second coding means 9 can be designed so as to guarantee that agiven data block DB, preferably the data block that occurs mostfrequently and which for example corresponds to the decimal value zero,is coded in that for this data block DB no coding signal et al, i.e. nocoding pulse KI, is generated and supplied, as a result of which nomodulation step at all is generated for this data block DB. This measureis advantageous in view of a reduction of the sideband level inconjunction with a so-called quasi-peak measurement.

[0028] The device 1 further includes selection means 10 which make itpossible to select that either the coding signals KI representing a datablock DB and supplied by the first coding means 4 or the coding signalsKI representing a data block DB and supplied by the second coding means9 can be applied to the amplitude modulation means 6.

[0029] In the present case the selection means 10 include a controlswitch 11, which is controllable by hand but which also be controllablein another manner. The control switch 11 has one end connected to apotential, not indicated, and has its other end connected to an input 12of the microcomputer 3. Arranged after the input 12 are control signalgenerating means 13, which are realized by means of the microcomputer 3and which generate two different control signals SS1 and SS2 independence on the switching state of the control switch 11. When thecontrol switch 11 is in its non-conductive switching state the controlsignal generating means 13 generate the first control signal SS1, whilein the conductive switching state of the control switch 11 said meansgenerate the second control signal SS2.

[0030] The selection means 10 further include controllable switchingmeans 14 arranged between, on the one hand, the first coding means 4 andthe second coding means 9 and, on the other hand, an output 15 of themicrocomputer 3, to which output the amplitude modulation means 6 areconnected. This means that the switching means 14 are included, on theone hand, the first coding means 4 and the second coding means 9 and, onthe other hand, the amplitude modulation means 6.

[0031] When the control switch 11 is in its switching state shown inFIG. 1 and, consequently, the control signal generating means 13 supplythe first control information SS1 to the control input 16 of theswitching means 14, this results in the switching means 14 being in theswitching state shown in FIG. 1, in which state the second coding means9 are connected to the amplitude modulation means 6.

[0032] When the second coding means 9 are connected to the amplitudemodulation means 6 via the switching means 14 this results in the pulsetrain shown in FIG. 2D being applied to the amplitude modulation means6, as a result of which the amplitude-modulated carrier signal TSM shownin FIG. 2E is generated, in which only one modulation step, namely themodulation step referenced MS225, occurs after the modulation step MS0initiated by the second start signal SP2.

[0033] As can be seen in FIG. 2E, the transmission of theamplitude-modulated carrier signal TSM corresponding to the data blockDB=225 dec shown in FIG. 2A requires a total transmission time of 4.833ms owing to the frame portion time T2 of 18.88 μs. In comparison withthe transmission time of 302.08 μs in FIG. 2 this is a substantiallylonger transmission time but in relation to the amplitude-modulatedcarrier signal TSM shown in FIG. 2 it is to be noted that in the timeinterval of 4.833 ms only a single modulation step occurs, namely themodulation step MS225, which has the advantageous result that theamplitude values in the range of the sidebands of the carrier signal TSare particularly small, so that no problems arise with statutoryregulations relating to the effects of spurious emission and thelimitation of spurious emission.

[0034] The device 1 described hereinbefore advantageously allows achoice between two coding methods, so that at option either a codingmethod can be selected in which comparatively high amplitudes occur inthe range of the sidebands of the carrier signal but which in anadvantageous manner guarantees high transmission rates, i.e. a rapidtransmission from the device to a transponder, or another coding methodcan be selected, which only permits a lower transmission rate, i.e. aslower transmission but which in an advantageous manner guaranteesparticularly small amplitude values in the range of the sidebands of thecarrier signal.

[0035] The device 1 shown in FIG. 23 differs from the device 1 shown inFIG. 1 in that it has selection means 10 by means of which it ispossible to select whether the coding pulses KI supplied by the firstcoding means 4 or by the second coding means 9 are transferred to theamplitude modulation means 6.

[0036] In the device 1 shown in FIG. 3 the selection means 10 alsoinclude the first coding means 4 and the second coding means 9. In thepresent case, the first coding means 4 and the second coding means 9each have a control input 17 and 18, respectively, which are arranged toreceive the control signals SS1 and SS2 supplied by the control signalgenerating means 13. Both coding means 4 and 9 are designed in such amanner that in the case that the first control signal SS1 is applied tothe control inputs 17 and 18 of the two coding means 4 and 9 the firstcoding means 4 are set to an inactive state and the second coding means9 are set to an active state, while in the case that the second controlsignal SS2 is applied to the control inputs 17 and 18 of the two codingmeans 4 and 9 the first coding means 4 are set to an active state andthe second coding means 9 are set to an inactive state. Thus, it is alsoachieved that when the control switch 11 is in its non-conductive statethe second coding means 9 supply the coding pulses KI generated by themto the amplitude modulation means 6 and when the control switch 11 is inits conductive state the first coding means 4 supply the coding pulsesKI generated by them to the amplitude modulation means 6. With regard tothe two devices 1 described hereinbefore it is to be noted that in thecase that for the transmission of data supplied by the data supply means2 not a single data block is used—as described hereinbefore for the sakeof simplicity—but that a data block sequence comprising a plurality ofdata blocks is required for this, which sequence for example consists ofn data blocks, the relevant coding means 4 or 9 only generate a startsignal SP1 or SP2 before the first data block of each of such data blocksequences.

[0037] The invention is not limited to the devices in accordance withthe two embodiments described hereinbefore by way of example. When thisis appropriate the second coding means may also be adapted to carry outa coding method in accordance with a “2-out-of-K” code or a “4-out-of-K”code. Moreover, when the first coding means are active a comparativelylow amplitude of the carrier signal may be selected, in which case onlya comparatively small transmission range can be obtained but it is alsoachieved that low amplitudes can be obtained in the range of thesidebands of the carrier signal. Furthermore, it is to be noted that, ifdesired, a device in accordance with the invention may also includethird coding means with the aid of which a third coding method can becarried out in order to apply coding signals coded in accordance with athird coding method to the amplitude modulation means for the purpose ofamplitude modulation of the carrier signal. It is to be noted thatinstead of amplitude modulation means other modulation means may beused, for example frequency modulation means or phase modulation means,enabling for example frequency shift keying or phase shift keying, forexample by 180°, to be carried out.

1. A write/read device (1) designed for the contactless communicationwith at least one transponder and comprising data supply means (2) forsupplying at least one data block (DB) and including first coding means(4), by which first coding means (4) a data block (DB) supplied by thedata supply means (2) and applied to said first coding means (4) can becoded in accordance with a first coding method and by which, as a resultof the coding in accordance with this first coding method, at the most agiven number N of coding signals (KI) representing a data block (DB) canbe generated and supplied, and including carrier signal generating means(5) for generating a carrier signal (TS) and including modulation means(6), to which modulation means (6) the carrier signal (TS) and thecoding signals (KI) can be applied and by which modulation means (6) thecarrier signal (TS) can be modulated in accordance with the codingsignals (KI) so as to generate and supply a modulated carrier signal(TSM) corresponding to the number of coding signals (KI) and having thesame number of modulation steps, and including transmission means (7),to which transmission means (7) the modulated carrier signal (TSM) canbe applied in order to be transmitted to at least one transponder,characterized in that there have been provided second coding means (9),by which second coding means (9) a data block (DB) supplied by the datasupply means (2) and applied to said second coding means (9) can becoded in accordance with a second coding method and by which secondcoding means (9), as a result of coding in accordance with said secondcoding method, at the most a given number M of coding signalsrepresenting a data block (DB) can be generated and supplied, the numberM being smaller than the number N, and there have been providedselection means (10), with the aid of which selection means (10) it ispossible to select that the coding signals (KI) representing a datablock (DB) and supplied by the first coding means (4) or that the codingsignals (KI) representing a data block (DB) and supplied by the secondcoding means (9) can be applied to the amplitude modulation means (6).2. A device (1) as claimed in claim 1, characterized in that the secondcoding means (9) are adapted to carry out a byte-oriented coding method.3. A device (1) as claimed in claim 2, characterized in that the secondcoding means (9) are adapted to carry out a coding method in accordancewith a “1-out-of-K” code.
 4. A device (1) as claimed in claim 1,characterized in that the selection means (10) include switching means(14) arranged between, on the one hand, the first coding means (4) andthe second coding means (9) and, on the other hand, the modulation means(6).
 5. A device (1) as claimed in claim 1, characterized in that thefirst coding means (4) are adapted to generate a first start signal(SP1) characteristic of the first coding method, which start signal canbe supplied by the first coding means (4) before the coding signals (KI)representing a data block (DB), the number of these coding signals beingat the most equal to the given number N.
 6. A device (1) as claimed inclaim 1, characterized in that the second coding means (9) are adaptedto generate a second start signal (SP2) characteristic of the secondcoding method, which start signal can be supplied by the second codingmeans (9) before the coding signals (KI) representing a data block (SB),the number of these coding signals being at the most equal to the givennumber M.